Our approach to the neurobiology of anxiety continues to be developmental with a focus on the role of early experience on the development of neurotransmitter and neuropeptide systems. We tested a specific hypothesis: that early stress activates brain corticotropin releasing factor (CRF) pathways and has long-term effects on brain CRF receptors with mixed results. As part of this project the development of CRF neurons, receptors, and second messenger was determined in fetal and postnatal rat brain. Receptors were found to be dramatically increased over adult levels soon after birth. Treating infants with CRF had short-term effects on development, long-term effects on behavior, but no lasting effects on brain CRF receptors. In related studies, neither noradrenergic lesions nor the behavioral paradigm of learned helplessness was found to alter brain CRF receptors.